It is known in the art to have photoelectric detection systems of transient objects through a target plane. It is also known to have moving life-size targets presented at which a projectile or missile is directed. Advantage is found, for example, in training security personnel in the use of firearms, presenting moving scenes that may be threatening to the personnel. Hall, U.S. Pat. No. 4,948,371, discloses such a system, including computer analysis of the accuracy of a shot at the target. In accordance with the effect of the shot, the scene changes to present a follow-on scene to which the user must react.
Such a real-time changing environment is also useful for sport training, such as golf and hunting, both with firearms and with arrows. In such a real-time scene, it is useful for training purposes to stop the scene at the time of arrival of the missile, such as an arrow, on the target with a marker superimposed on the still scene to indicate a hit location. Dart, U.S. Pat. No. 5,328,190 discloses such a system. Dart uses an invisible infrared light source at the base of a target screen directed upward in front of the screen to flood a plane orthogonal to an intended missile flight path. Thus, when a missile passes arrives at the screen, IR light reflects off of the missile to a detector camera spaced apart in front of the screen.
Because of the variable reflectivity of various missile types, reflector systems lack the consistency, reliability, and versatility of active systems, that is, systems that depend only on the interruption of light caused by a missile shadowing a sensor. A reflective system also cannot use visible light from the projected scene, or light from the projected scene would reflect from the missile and cause false alarm detections; it must therefore employ invisible, e.g. infrared, light that is not detected by the system camera sensitive only to visible wavelengths. This design restrictions unduly limits the system, for example, in maintaining an accurately aligned system. Because the system inherently requires an accurate assessment of a missile shot as compared to a projected target scene, it is essential that the system be accurately and frequently aligned and calibrated. Thus, the system should be easy and quick to align. Because IR light is not discernible to the human eye, it is difficult to align or to detect conditions out of alignment. The accuracy of the system is therefore always in question and its viability is unreliable.